[llvm] [LFI][Doc] Update documentation for planned features (PR #192128)

[Nick Desaulniers via llvm-commits]

================
@@ -319,10 +348,10 @@ used for branching into the runtime.
 |                 |                              |
 +-----------------+------------------------------+
 
-Thread-local storage
-~~~~~~~~~~~~~~~~~~~~
+Thread pointer
+~~~~~~~~~~~~~~
 
-TLS accesses are rewritten into loads/stores from the context register
+TP accesses are rewritten into loads/stores from the context register
----------------
nickdesaulniers wrote:

```suggestion
Thread pointer (TP)
~~~~~~~~~~~~~~

TP accesses are rewritten into loads/stores from the context register
```

https://github.com/llvm/llvm-project/pull/192128